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Updated documentation in PredictionMode

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Sam Harwell 2013-01-03 04:03:34 -06:00
parent 98d2ba8fb5
commit d95cdab065
1 changed files with 384 additions and 234 deletions
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runtime/Java/src/org/antlr/v4/runtime/atn/PredictionMode.java
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@ -96,92 +96,138 @@ public enum PredictionMode {
}
/**
SLL prediction termination.
There are two cases: the usual combined SLL+LL parsing and
pure SLL parsing that has no fail over to full LL.
COMBINED SLL+LL PARSING
SLL can decide to give up any point, even immediately,
failing over to full LL. To be as efficient as possible,
though, SLL should fail over only when it's positive it can't get
anywhere on more lookahead without seeing a conflict.
Assuming combined SLL+LL parsing, an SLL confg set with only
conflicting subsets should failover to full LL, even if the
config sets don't resolve to the same alternative like {1,2}
and {3,4}. If there is at least one nonconflicting set of
configs, SLL could continue with the hopes that more lookahead
will resolve via one of those nonconflicting configs.
Here's the prediction termination rule them: SLL (for SLL+LL
parsing) stops when it sees only conflicting config subsets.
In contrast, full LL keeps going when there is uncertainty.
HEURISTIC
As a heuristic, we stop prediction when we see any conflicting subset
unless we see a state that only has one alternative associated with
it. The single-alt-state thing lets prediction continue upon rules
like (otherwise, it would admit defeat too soon):
// [12|1|[], 6|2|[], 12|2|[]].
s : (ID | ID ID?) ';' ;
When the ATN simulation reaches the state before ';', it has a DFA
state that looks like: [12|1|[], 6|2|[], 12|2|[]]. Naturally 12|1|[]
and 12|2|[] conflict, but we cannot stop processing this node because
alternative to has another way to continue, via [6|2|[]].
It also let's us continue for this rule:
// [1|1|[], 1|2|[], 8|3|[]]
a : A | A | A B ;
After matching input A, we reach the stop state for rule A, state 1.
State 8 is the state right before B. Clearly alternatives 1 and 2
conflict and no amount of further lookahead will separate the two.
However, alternative 3 will be able to continue and so we do not stop
working on this state. In the previous example, we're concerned with
states associated with the conflicting alternatives. Here alt 3 is not
associated with the conflicting configs, but since we can continue
looking for input reasonably, don't declare the state done.
PURE SLL PARSING
To handle pure SLL parsing, all we have to do is make sure that we
combine stack contexts for configurations that differ only by semantic
predicate. From there, we can do the usual SLL termination heuristic.
PREDICATES IN SLL+LL PARSING
SLL decisions don't evaluate predicates until after they reach DFA
stop states because they need to create the DFA cache that
works in all (semantic) situations. (In contrast, full LL
evaluates predicates collected during start state computation
so it can ignore predicates thereafter.) This means that SLL
termination detection can totally ignore semantic predicates.
Of course, implementation-wise, ATNConfigSets combine stack
contexts but not semantic predicate contexts so we might see
two configs like this:
(s, 1, x, {}), (s, 1, x', {p})
Before testing these configurations against others, we have
to merge x and x' (w/o modifying the existing configs). For
example, we test (x+x')==x'' when looking for conflicts in
the following configs.
(s, 1, x, {}), (s, 1, x', {p}), (s, 2, x'', {})
If the configuration set has predicates, which we can test
quickly, this algorithm makes a copy of the configs and
strip out all of the predicates so that a standard
ATNConfigSet will merge everything ignoring
predicates.
*/
* Computes the SLL prediction termination condition.
*
* <p/>
*
* This method computes the SLL prediction termination condition for both of
* the following cases.
*
* <ul>
* <li>The usual SLL+LL fallback upon SLL conflict</li>
* <li>Pure SLL without LL fallback</li>
* </ul>
*
* <p/>
*
* <strong>COMBINED SLL+LL PARSING</strong>
*
* <p/>
*
* When LL-fallback is enabled upon SLL conflict, correct predictions are
* ensured regardless of how the termination condition is computed by this
* method. Due to the substantially higher cost of LL prediction, the
* prediction should only fall back to LL when the additional lookahead
* cannot lead to a unique SLL prediction.
*
* <p/>
*
* Assuming combined SLL+LL parsing, an SLL configuration set with only
* conflicting subsets should fall back to full LL, even if the
* configuration sets don't resolve to the same alternative (e.g.
* {@code {1,2}} and {@code {3,4}}. If there is at least one non-conflicting
* configuration, SLL could continue with the hopes that more lookahead will
* resolve via one of those non-conflicting configurations.
*
* <p/>
*
* Here's the prediction termination rule them: SLL (for SLL+LL parsing)
* stops when it sees only conflicting configuration subsets. In contrast,
* full LL keeps going when there is uncertainty.
*
* <p/>
*
* <strong>HEURISTIC</strong>
*
* <p/>
*
* As a heuristic, we stop prediction when we see any conflicting subset
* unless we see a state that only has one alternative associated with it.
* The single-alt-state thing lets prediction continue upon rules like
* (otherwise, it would admit defeat too soon):
*
* <p/>
*
* {@code [12|1|[], 6|2|[], 12|2|[]]. s : (ID | ID ID?) ';' ;}
*
* <p/>
*
* When the ATN simulation reaches the state before {@code ';'}, it has a
* DFA state that looks like: {@code [12|1|[], 6|2|[], 12|2|[]]}. Naturally
* {@code 12|1|[]} and {@code 12|2|[]} conflict, but we cannot stop
* processing this node because alternative to has another way to continue,
* via {@code [6|2|[]]}.
*
* <p/>
*
* It also let's us continue for this rule:
*
* <p/>
*
* {@code [1|1|[], 1|2|[], 8|3|[]] a : A | A | A B ;}
*
* <p/>
*
* After matching input A, we reach the stop state for rule A, state 1.
* State 8 is the state right before B. Clearly alternatives 1 and 2
* conflict and no amount of further lookahead will separate the two.
* However, alternative 3 will be able to continue and so we do not stop
* working on this state. In the previous example, we're concerned with
* states associated with the conflicting alternatives. Here alt 3 is not
* associated with the conflicting configs, but since we can continue
* looking for input reasonably, don't declare the state done.
*
* <p/>
*
* <strong>PURE SLL PARSING</strong>
*
* <p/>
*
* To handle pure SLL parsing, all we have to do is make sure that we
* combine stack contexts for configurations that differ only by semantic
* predicate. From there, we can do the usual SLL termination heuristic.
*
* <p/>
*
* <strong>PREDICATES IN SLL+LL PARSING</strong>
*
* <p/>
*
* SLL decisions don't evaluate predicates until after they reach DFA stop
* states because they need to create the DFA cache that works in all
* semantic situations. In contrast, full LL evaluates predicates collected
* during start state computation so it can ignore predicates thereafter.
* This means that SLL termination detection can totally ignore semantic
* predicates.
*
* <p/>
*
* Implementation-wise, {@link ATNConfigSet} combines stack contexts but not
* semantic predicate contexts so we might see two configurations like the
* following.
*
* <p/>
*
* {@code (s, 1, x, {}), (s, 1, x', {p})}
*
* <p/>
*
* Before testing these configurations against others, we have to merge
* {@code x} and {@code x'} (without modifying the existing configurations).
* For example, we test {@code (x+x')==x''} when looking for conflicts in
* the following configurations.
*
* <p/>
*
* {@code (s, 1, x, {}), (s, 1, x', {p}), (s, 2, x'', {})}
*
* <p/>
*
* If the configuration set has predicates (as indicated by
* {@link ATNConfigSet#hasSemanticContext}), this algorithm makes a copy of
* the configurations to strip out all of the predicates so that a standard
* {@link ATNConfigSet} will merge everything ignoring predicates.
*/
public static boolean hasSLLConflictTerminatingPrediction(PredictionMode mode, @NotNull ATNConfigSet configs) {
/* Configs in rule stop states indicate reaching the end of the decision
* rule (local context) or end of start rule (full context). If all
@ -258,145 +304,211 @@ public enum PredictionMode {
}
/**
Full LL prediction termination.
Can we stop looking ahead during ATN simulation or is there some
uncertainty as to which alternative we will ultimately pick, after
consuming more input? Even if there are partial conflicts, we might
know that everything is going to resolve to the same minimum
alt. That means we can stop since no more lookahead will change that
fact. On the other hand, there might be multiple conflicts that
resolve to different minimums. That means we need more look ahead to
decide which of those alternatives we should predict.
The basic idea is to split the set of configurations, C, into
conflicting (s, _, ctx, _) subsets and singleton subsets with
non-conflicting configurations. Two config's conflict if they have
identical state and rule stack contexts but different alternative
numbers: (s, i, ctx, _), (s, j, ctx, _) for i!=j.
Reduce these config subsets to the set of possible alternatives. You
can compute the alternative subsets in one go as follows:
A_s,ctx = {i | (s, i, ctx, _) for in C holding s, ctx fixed}
Or in pseudo-code:
for c in C:
map[c] U= c.alt # map hash/equals uses s and x, not alt and not pred
Then map.values is the set of A_s,ctx sets.
If |A_s,ctx|=1 then there is no conflict associated with s and ctx.
Reduce the subsets to singletons by choosing a minimum of each subset.
If the union of these alternatives sets is a singleton, then no amount
of more lookahead will help us. We will always pick that
alternative. If, however, there is more than one alternative, then we
are uncertain which alt to predict and must continue looking for
resolution. We may or may not discover an ambiguity in the future,
even if there are no conflicting subsets this round.
The biggest sin is to terminate early because it means we've made a
decision but were uncertain as to the eventual outcome. We haven't
used enough lookahead. On the other hand, announcing a conflict too
late is no big deal; you will still have the conflict. It's just
inefficient. It might even look until the end of file.
Semantic predicates for full LL aren't involved in this decision
because the predicates are evaluated during start state computation.
This set of configurations was derived from the initial subset with
configurations holding false predicate stripped out.
CONFLICTING CONFIGS
Two configurations, (s, i, x) and (s, j, x'), conflict when i!=j but
x = x'. Because we merge all (s, i, _) configurations together, that
means that there are at most n configurations associated with state s
for n possible alternatives in the decision. The merged stacks
complicate the comparison of config contexts, x and x'. Sam checks to
see if one is a subset of the other by calling merge and checking to
see if the merged result is either x or x'. If the x associated with
lowest alternative i is the superset, then i is the only possible
prediction since the others resolve to min i as well. If, however, x
is associated with j>i then at least one stack configuration for j is
not in conflict with alt i. The algorithm should keep going, looking
for more lookahead due to the uncertainty.
For simplicity, I'm doing a equality check between x and x' that lets
the algorithm continue to consume lookahead longer than necessary.
The reason I like the equality is of course the simplicity but also
because that is the test you need to detect the alternatives that are
actually in conflict.
CONTINUE/STOP RULE
Continue if union of resolved alt sets from nonconflicting and
conflicting alt subsets has more than one alt. We are uncertain about
which alternative to predict.
The complete set of alternatives, [i for (_,i,_)], tells us
which alternatives are still in the running for the amount of input
we've consumed at this point. The conflicting sets let us to strip
away configurations that won't lead to more states (because we
resolve conflicts to the configuration with a minimum alternate for
given conflicting set.)
CASES:
* no conflicts & > 1 alt in set => continue
* (s, 1, x), (s, 2, x), (s, 3, z)
(s', 1, y), (s', 2, y)
yields nonconflicting set {3} U conflicting sets min({1,2}) U min({1,2}) = {1,3}
=> continue
* (s, 1, x), (s, 2, x),
(s', 1, y), (s', 2, y)
(s'', 1, z)
yields nonconflicting set you this {1} U conflicting sets min({1,2}) U min({1,2}) = {1}
=> stop and predict 1
* (s, 1, x), (s, 2, x),
(s', 1, y), (s', 2, y)
yields conflicting, reduced sets {1} U {1} = {1}
=> stop and predict 1, can announce ambiguity {1,2}
* (s, 1, x), (s, 2, x)
(s', 2, y), (s', 3, y)
yields conflicting, reduced sets {1} U {2} = {1,2}
=> continue
* (s, 1, x), (s, 2, x)
(s', 3, y), (s', 4, y)
yields conflicting, reduced sets {1} U {3} = {1,3}
=> continue
EXACT AMBIGUITY DETECTION
If all states report the same conflicting alt set, then we know we
have the real ambiguity set:
|A_i|>1 and A_i = A_j for all i, j.
In other words, we continue examining lookahead until all A_i have
more than one alt and all A_i are the same. If A={{1,2}, {1,3}}, then
regular LL prediction would terminate because the resolved set is
{1}. To determine what the real ambiguity is, we have to know whether
the ambiguity is between one and two or one and three so we keep
going. We can only stop prediction when we need exact ambiguity
detection when the sets look like A={{1,2}} or {{1,2},{1,2}} etc...
* Full LL prediction termination.
*
* <p/>
*
* Can we stop looking ahead during ATN simulation or is there some
* uncertainty as to which alternative we will ultimately pick, after
* consuming more input? Even if there are partial conflicts, we might know
* that everything is going to resolve to the same minimum alternative. That
* means we can stop since no more lookahead will change that fact. On the
* other hand, there might be multiple conflicts that resolve to different
* minimums. That means we need more look ahead to decide which of those
* alternatives we should predict.
*
* <p/>
*
* The basic idea is to split the set of configurations {@code C}, into
* conflicting subsets {@code (s, _, ctx, _)} and singleton subsets with
* non-conflicting configurations. Two configurations conflict if they have
* identical {@link ATNConfig#state} and {@link ATNConfig#context} values
* but different {@link ATNConfig#alt} value, e.g. {@code (s, i, ctx, _)}
* and {@code (s, j, ctx, _)} for {@code i!=j}.
*
* <p/>
*
* Reduce these configuration subsets to the set of possible alternatives.
* You can compute the alternative subsets in one pass as follows:
*
* <p/>
*
* {@code A_s,ctx = {i | (s, i, ctx, _)}} for each configuration in
* {@code C} holding {@code s} and {@code ctx} fixed.
*
* <p/>
*
* Or in pseudo-code, for each configuration {@code c} in {@code C}:
*
* <pre>
* map[c] U= c.{@link ATNConfig#alt alt} # map hash/equals uses s and x, not
* alt and not pred
* </pre>
*
* <p/>
*
* The values in {@code map} are the set of {@code A_s,ctx} sets.
*
* <p/>
*
* If {@code |A_s,ctx|=1} then there is no conflict associated with
* {@code s} and {@code ctx}.
*
* <p/>
*
* Reduce the subsets to singletons by choosing a minimum of each subset. If
* the union of these alternative subsets is a singleton, then no amount of
* more lookahead will help us. We will always pick that alternative. If,
* however, there is more than one alternative, then we are uncertain which
* alternative to predict and must continue looking for resolution. We may
* or may not discover an ambiguity in the future, even if there are no
* conflicting subsets this round.
*
* <p/>
*
* The biggest sin is to terminate early because it means we've made a
* decision but were uncertain as to the eventual outcome. We haven't used
* enough lookahead. On the other hand, announcing a conflict too late is no
* big deal; you will still have the conflict. It's just inefficient. It
* might even look until the end of file.
*
* <p/>
*
* No special consideration for semantic predicates is required because
* predicates are evaluated on-the-fly for full LL prediction, ensuring that
* no configuration contains a semantic context during the termination
* check.
*
* <p/>
*
* <strong>CONFLICTING CONFIGS</strong>
*
* <p/>
*
* Two configurations {@code (s, i, x)} and {@code (s, j, x')}, conflict
* when {@code i!=j} but {@code x=x'}. Because we merge all
* {@code (s, i, _)} configurations together, that means that there are at
* most {@code n} configurations associated with state {@code s} for
* {@code n} possible alternatives in the decision. The merged stacks
* complicate the comparison of configuration contexts {@code x} and
* {@code x'}. Sam checks to see if one is a subset of the other by calling
* merge and checking to see if the merged result is either {@code x} or
* {@code x'}. If the {@code x} associated with lowest alternative {@code i}
* is the superset, then {@code i} is the only possible prediction since the
* others resolve to {@code min(i)} as well. However, if {@code x} is
* associated with {@code j>i} then at least one stack configuration for
* {@code j} is not in conflict with alternative {@code i}. The algorithm
* should keep going, looking for more lookahead due to the uncertainty.
*
* <p/>
*
* For simplicity, I'm doing a equality check between {@code x} and
* {@code x'} that lets the algorithm continue to consume lookahead longer
* than necessary. The reason I like the equality is of course the
* simplicity but also because that is the test you need to detect the
* alternatives that are actually in conflict.
*
* <p/>
*
* <strong>CONTINUE/STOP RULE</strong>
*
* <p/>
*
* Continue if union of resolved alternative sets from non-conflicting and
* conflicting alternative subsets has more than one alternative. We are
* uncertain about which alternative to predict.
*
* <p/>
*
* The complete set of alternatives, {@code [i for (_,i,_)]}, tells us which
* alternatives are still in the running for the amount of input we've
* consumed at this point. The conflicting sets let us to strip away
* configurations that won't lead to more states because we resolve
* conflicts to the configuration with a minimum alternate for the
* conflicting set.
*
* <p/>
*
* <strong>CASES</strong>
*
* <ul>
*
* <li>no conflicts and more than 1 alternative in set =&gt; continue</li>
*
* <li> {@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s, 3, z)},
* {@code (s', 1, y)}, {@code (s', 2, y)} yields non-conflicting set
* {@code {3}} U conflicting sets {@code min({1,2})} U {@code min({1,2})} =
* {@code {1,3}} =&gt; continue
* </li>
*
* <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 1, y)},
* {@code (s', 2, y)}, {@code (s'', 1, z)} yields non-conflicting set
* {@code {1}} U conflicting sets {@code min({1,2})} U {@code min({1,2})} =
* {@code {1}} =&gt; stop and predict 1</li>
*
* <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 1, y)},
* {@code (s', 2, y)} yields conflicting, reduced sets {@code {1}} U
* {@code {1}} = {@code {1}} =&gt; stop and predict 1, can announce
* ambiguity {@code {1,2}}</li>
*
* <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 2, y)},
* {@code (s', 3, y)} yields conflicting, reduced sets {@code {1}} U
* {@code {2}} = {@code {1,2}} =&gt; continue</li>
*
* <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 3, y)},
* {@code (s', 4, y)} yields conflicting, reduced sets {@code {1}} U
* {@code {3}} = {@code {1,3}} =&gt; continue</li>
*
* </ul>
*
* <strong>EXACT AMBIGUITY DETECTION</strong>
*
* <p/>
*
* If all states report the same conflicting set of alternatives, then we
* know we have the exact ambiguity set.
*
* <p/>
*
* <code>|A_<em>i</em>|&gt;1</code> and
* <code>A_<em>i</em> = A_<em>j</em></code> for all <em>i</em>, <em>j</em>.
*
* <p/>
*
* In other words, we continue examining lookahead until all {@code A_i}
* have more than one alternative and all {@code A_i} are the same. If
* {@code A={{1,2}, {1,3}}}, then regular LL prediction would terminate
* because the resolved set is {@code {1}}. To determine what the real
* ambiguity is, we have to know whether the ambiguity is between one and
* two or one and three so we keep going. We can only stop prediction when
* we need exact ambiguity detection when the sets look like
* {@code A={{1,2}}} or {@code {{1,2},{1,2}}}, etc...
*/
public static int resolvesToJustOneViableAlt(Collection<BitSet> altsets) {
public static int resolvesToJustOneViableAlt(@NotNull Collection<BitSet> altsets) {
return getSingleViableAlt(altsets);
}
public static boolean allSubsetsConflict(Collection<BitSet> altsets) {
/**
* Determines if every alternative subset in {@code altsets} contains more
* than one alternative.
*
* @param altsets a collection of alternative subsets
* @return {@code true} if every {@link BitSet} in {@code altsets} has
* {@link BitSet#cardinality cardinality} &gt; 1, otherwise {@code false}
*/
public static boolean allSubsetsConflict(@NotNull Collection<BitSet> altsets) {
return !hasNonConflictingAltSet(altsets);
}
/** return (there exists len(A_i)==1 for some A_i in altsets A) */
public static boolean hasNonConflictingAltSet(Collection<BitSet> altsets) {
/**
* Determines if any single alternative subset in {@code altsets} contains
* exactly one alternative.
*
* @param altsets a collection of alternative subsets
* @return {@code true} if {@code altsets} contains a {@link BitSet} with
* {@link BitSet#cardinality cardinality} 1, otherwise {@code false}
*/
public static boolean hasNonConflictingAltSet(@NotNull Collection<BitSet> altsets) {
for (BitSet alts : altsets) {
if ( alts.cardinality()==1 ) {
return true;
@ -405,8 +517,15 @@ public enum PredictionMode {
return false;
}
/** return (there exists len(A_i)>1 for some A_i in altsets A) */
public static boolean hasConflictingAltSet(Collection<BitSet> altsets) {
/**
* Determines if any single alternative subset in {@code altsets} contains
* more than one alternative.
*
* @param altsets a collection of alternative subsets
* @return {@code true} if {@code altsets} contains a {@link BitSet} with
* {@link BitSet#cardinality cardinality} &gt; 1, otherwise {@code false}
*/
public static boolean hasConflictingAltSet(@NotNull Collection<BitSet> altsets) {
for (BitSet alts : altsets) {
if ( alts.cardinality()>1 ) {
return true;
@ -415,7 +534,14 @@ public enum PredictionMode {
return false;
}
public static boolean allSubsetsEqual(Collection<BitSet> altsets) {
/**
* Determines if every alternative subset in {@code altsets} is equivalent.
*
* @param altsets a collection of alternative subsets
* @return {@code true} if every member of {@code altsets} is equal to the
* others, otherwise {@code false}
*/
public static boolean allSubsetsEqual(@NotNull Collection<BitSet> altsets) {
Iterator<BitSet> it = altsets.iterator();
BitSet first = it.next();
while ( it.hasNext() ) {
@ -425,14 +551,28 @@ public enum PredictionMode {
return true;
}
public static int getUniqueAlt(Collection<BitSet> altsets) {
/**
* Returns the unique alternative predicted by all alternative subsets in
* {@code altsets}. If no such alternative exists, this method returns
* {@link ATN#INVALID_ALT_NUMBER}.
*
* @param altsets a collection of alternative subsets
*/
public static int getUniqueAlt(@NotNull Collection<BitSet> altsets) {
BitSet all = getAlts(altsets);
if ( all.cardinality()==1 ) return all.nextSetBit(0);
return ATN.INVALID_ALT_NUMBER;
}
public static BitSet getAlts(Collection<BitSet> altsets) {
/**
* Gets the complete set of represented alternatives for a collection of
* alternative subsets. This method returns the union of each {@link BitSet}
* in {@code altsets}.
*
* @param altsets a collection of alternative subsets
* @return the set of represented alternatives in {@code altsets}
*/
public static BitSet getAlts(@NotNull Collection<BitSet> altsets) {
BitSet all = new BitSet();
for (BitSet alts : altsets) {
all.or(alts);
@ -441,10 +581,15 @@ public enum PredictionMode {
}
/**
* This function gets the conflicting alt subsets from a configuration set.
* for c in configs:
* map[c] U= c.alt # map hash/equals uses s and x, not alt and not pred
*/
* This function gets the conflicting alt subsets from a configuration set.
* For each configuration {@code c} in {@code configs}:
*
* <pre>
* map[c] U= c.{@link ATNConfig#alt alt} # map hash/equals uses s and x, not
* alt and not pred
* </pre>
*/
@NotNull
public static Collection<BitSet> getConflictingAltSubsets(ATNConfigSet configs) {
AltAndContextMap configToAlts = new AltAndContextMap();
for (ATNConfig c : configs) {
@ -458,11 +603,16 @@ public enum PredictionMode {
return configToAlts.values();
}
/** Get a map from state to alt subset from a configuration set.
* for c in configs:
* map[c.state] U= c.alt
/**
* Get a map from state to alt subset from a configuration set. For each
* configuration {@code c} in {@code configs}:
*
* <pre>
* map[c.{@link ATNConfig#state state}] U= c.{@link ATNConfig#alt alt}
* </pre>
*/
public static Map<ATNState, BitSet> getStateToAltMap(ATNConfigSet configs) {
@NotNull
public static Map<ATNState, BitSet> getStateToAltMap(@NotNull ATNConfigSet configs) {
Map<ATNState, BitSet> m = new HashMap<ATNState, BitSet>();
for (ATNConfig c : configs) {
BitSet alts = m.get(c.state);
@ -475,7 +625,7 @@ public enum PredictionMode {
return m;
}
public static boolean hasStateAssociatedWithOneAlt(ATNConfigSet configs) {
public static boolean hasStateAssociatedWithOneAlt(@NotNull ATNConfigSet configs) {
Map<ATNState, BitSet> x = getStateToAltMap(configs);
for (BitSet alts : x.values()) {
if ( alts.cardinality()==1 ) return true;
@ -483,7 +633,7 @@ public enum PredictionMode {
return false;
}
public static int getSingleViableAlt(Collection<BitSet> altsets) {
public static int getSingleViableAlt(@NotNull Collection<BitSet> altsets) {
BitSet viableAlts = new BitSet();
for (BitSet alts : altsets) {
int minAlt = alts.nextSetBit(0);